This invention relates to a lock and key system equipped with means for identifying a key used with such a cylinder lock for automotive vehicles or other applications.
Electronic lock and key systems for anti-theft purposes for doors of an automotive vehicle have been proposed, for example, by Japanese Provisional Patent Publication (Kokai) No. 55-155879, in which a key is provided with a code formed by magnetic means, and only when electronic means senses the key to be a proper one, a lock is unlocked.
As another example of such electronic lock and key system, U.S. Pat. No. 3,355,631 discloses a key actuated control circuit which has a detecting circuit comprising a reference oscillator, a plurality of LC oscillators connected in parallel with each other and to output terminals of the reference oscillator, and a key having a plurality of magnetic slugs arranged at regular intervals. The key actuated control circuit is constructed such that when the key is inserted in a key receptacle the slugs in the key cause the inductances of the coils of the respective corresponding LC oscillators to change, and only if the changed inductances of all the LC oscillators are tuned to the frequency of the reference oscillator, an oscillation signal is outputted to thereby effect unlocking.
However, a problem with this key control circuit is that to manufacture keys with different characteristics (codes) it is necessary to set the characteristics of slugs, by taking into consideration the frequencies of respective corresponding LC oscillators, wherefore the setting is complicated, making it difficult to manufacture keys with the same code. Besides, since each key has a plurality of magnetic slugs corresponding to respective L/C oscillators, a limitation is imposed upon increasing the number of key codes.
Further, according to U.S. Pat. No. 3,355,631, the manufacture of the L/C oscillators has to be strictly controlled so that each L/C oscillator generates an exact frequency, because otherwise erroneous key identification results.
Further, the construction of Japanese Provisional Patent Publication (Kokai) No. 55-155879 referred to hereinbefore, for example, cannot absolutely prevent socalled picking, i.e. forced unlocking of the door lock, breakage of the door lock, etc., even when the electronic means is operating to prohibit unlocking of the door lock, for the following reason: If a thief operates a rotor of the door lock without using the proper key but by means of a special tool, etc., he can rotate a cam lever provided on an end of the rotor to thereby rotate a locking lever of the door lock which is connected to the cam lever via an interlocking rod.
Also, there is known an electronic lock and key system equipped with remote control means for doors of automotive vehicles, for example, from U.S. Pat. No. 4,258,352, according to which the system comprises a transmitter for transmitting a coded message, a receiver (key sensor) provided in the vehicle for receiving the coded message from the transmitter, and a comparator for outputting a signal commanding unlocking the door lock only when the received coded message agrees with a preset reference coded message.
However, a problem with this system is that when the transmitter goes out of order or runs out of electric supply (due to exhaustion of the battery), it cannot output the signal to unlock the door lock.
In order to solve these problems, Japanese Provisional Utility Model Publication (Kokai) No. 61-166067, for example, has proposed a system wherein an infrared ray is employed as medium for transmission of the coded message. That is, an infrared-ray transmitter is incorporated in a key for a lock in a door of the vehicle in a manner making it possible to selectively unlock the lock, by means of the transmitter or by manually operating the key.
However, according to this prior art, since it is possible to unlock the door with the key, the system is not safe from illegal unlocking by so-called picking breakage of the door lock, etc., so that this system cannot perfectly guarantee prevention of theft.